1. Technical Field
The present invention relates to motors for driving storage disks in order to drive, for example, hard disks and like storage disks, as well as to storage disk drive devices provided with the motors. In particular the present invention relates to a motor, and to a storage-disk drive device for rotary-driving storage disks with the motor, wherein fluid dynamic pressure bearings function to support the rotor rotatively against the stator element.
2. Description of Related Art
Motors, and storage-disk drive devices for rotary-driving storage disks with the motors, have been known conventionally wherein fluid dynamic pressure bearings are employed for relative, rotational support of a shaft and a sleeve member encompassing the shaft.
Japanese Laid-Open Patent Application No. 10-267036 discloses a storage disk drive motor used in a disk drive device. The disk drive motor includes a bracket, a cylindrical sleeve fixedly attached to the approximate center of the bracket, a shaft inserted within the sleeve, and a rotor hub fixed to one end of the shaft for integrally rotating with the shaft. A rotor magnet is attached to the inner peripheral surface of the rotor hub. A stator is disposed on the bracket so as to oppose the rotor magnet in the radial direction, and such that the magnetic centers of the rotor magnet and the stator are set apart axially, i.e., not coincident. As a means for supporting the radial load, the motor also has a pair of radial bearings formed by the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve, at an axial separation. At the same time, as a means for supporting the thrust (axial) load, the motor also has a thrust bearing formed by an end face of the shaft, and a thrust plate that occludes the bottom portion of the sleeve and axially opposes the shaft end face.
When electric current is supplied to the stator in conventional disk-drive motors, a rotating magnetic field is generated between the rotor magnet and the stator, which rotates the rotor hub in a predetermined direction. When the rotor hub rotates, a lubricating fluid flows in a predetermined direction through dynamic-pressure generating grooves in the radial and thrust bearings, which develops dynamic pressure that supports the rotor hub axially against the shaft.
Further, by forming the thrust bearing portion on the end face of the shaft and the thrust plate only, pressure for supporting the thrust load acts unidirectionally only, in the axial direction. Meanwhile the magnetic centers of the rotor magnet and the stator are at an axial displacement, which compels a magnetic attractive force between the rotor magnet and the bracket, by which the magnetic attractive force and the thrust load-bearing pressure of the thrust bearing are balanced.
In conventional disk-drive devices, as in the foregoing, the magnetic attractive force between the rotor magnet and the stator is in balance with the thrust load bearing pressure acting in the axial direction unidirectionally only. Nevertheless, when the motor rotates at low speed, or is accelerating/decelerating, the thrust load bearing pressure does not balance the magnetic attractive force. Out of balance the magnetic attractive force is exaggerated and brings bearing component parts into contact, leading to their progressive detrition. As a result, the reliability of the motor deteriorates.
Personal computers employing storage disk drive devices driven by conventional motors continue to be made smaller and thinner. Thus the motors that rotate the storage disk in such disk drives presumably are to be made smaller and thinner as well. The magnetic attractive force acting between the stator and rotor magnet establishes a balancing mechanism between the two in their axial opposition. The axial positions and tilt of the stator and rotor magnet affect the magnetic attractive force, however, making this balancing mechanism unsuitable for thinner-type disk drive devices, which require high precision in assembly to maintain stability in device performance.
Other conventional fluid dynamic pressure bearings are known, such as is disclosed in Japanese Laid-Open Patent Application No. 10-69713. Therein a rotor magnet axially opposes the stator, and dynamic pressure-generating grooves are formed superficially on one end of the shaft, without a thrust plate being employed.
The motor employs fluid dynamic pressure bearings for rotary support of the rotor hub without contact. In this case, since the rotor magnet and stator are arranged in axial opposition, during rotation of the motor magnetic attractive and repulsive forces repeatedly occur, which destabilizes the rotor hub rotation.
Where these conventional motors thus requiring rotor magnets are employed in a hard-disk drive, magnetic powder or particles produced when the magnet is formed or during motor assembly is liable to stick to the recording surface of the storage disk that the motor drives, or to the disk magnetic data read/write head. This causes magnetic contamination that hinders correct reading and writing of data, or worse, destroys data recorded on the disk. Further, the expense of the magnet itself increases the cost of motors in which such magnets are used, and of storage disk drive devices employing the motors.
An object of the present invention is to provide a thin storage disk drive motor.
Another object is to provide a storage disk drive motor that is simple in construction and operates with sufficient stability.
A further object of the present invention is to provide a storage disk drive motor which is manufactured and assembled easily.
A yet other object of the invention is to provide a storage disk drive motor the manufacturing costs of which are reduced.
A yet further object is to configure a storage disk drive motor for low electric-power consumption.
Further, an object of the present invention to configure a storage disk drive device furnished with a storage disk drive motor that is made thin, is readily manufactured and assembled, and moreover inexpensive, and at the same time is low power-consuming.
A still further object of the present invention is to provide a thin motor that is simple in construction and operates with high stability.
A still another object of the present invention is to provide a disk drive device which is thin and reliable due to thinness and stability of a disk drive motor provided therein.
A still other object of the present invention is to provide a thin reluctance motor that is simple in construction and operates with high stability.
A storage disk drive motor of the present invention is provided with: a stationary member; a rotary member on which at least one storage disk is loaded for rotating freely relative to the stationary member; and a thrust bearing generating thrust load-supporting pressure in response to rotation of the rotary member. A plurality of projections jutting axially inward is provided on the rotary member and a stator is provided on the stationary member so as to oppose axially the aforesaid plurality of projections. Electro-magnetic force arising due to energization and/or excitation in the stator magnetically attracts the rotary member axially inward. The thrust bearing generates thrust load-bearing pressure that acts axially outward only, which balances the magnetic attractive force by the stator for the rotary member and the thrust load-bearing pressure that develops in the thrust bearing.
The storage disk drive motor of the present invention is furnished with a plurality of salient poles jutting axially inward on the bottom face of the rotary member, and is organized in a so-called axial-gap type motor construction wherein the stator and the salient poles oppose axially. At the same time a so-called reluctance type motor construction is established, wherein the motor gains rotational power through excitation of the stator to magnetically attract the salient poles provided on the bottom face of the rotary member. Therefore, the electromotive force of the stator magnetically attracts the rotary member axially, balancing it with the thrust load-bearing pressure generated in the thrust bearing, acting axially outward only. In addition, rotor magnets being unnecessary for reluctance-type motors curtails the number of parts, reduces costs, and at the same time prevents magnetic contamination caused by magnetic powder and/or particles from the motor from occurring.
Preferably, the salient poles are formed integrally with the rotary member, which is made from a magnetic material. Wherein the rotary member is to be made from an non-magnetic material, the salient poles can be formed by laminating a plurality of thin, wafer-shaped magnetic elements, fitted with a means for fastening them to the bottom face of the rotary member.
Forming the thrust bearing between the upper end-face of a sleeve of the stationary member and the bottom face of the rotary member also enables slimming down of the storage disk drive motor, while maintenance of posturexe2x80x94e.g., of the core deflectionxe2x80x94when the rotary member rotates is controlled with a radial bearing generating radial load-supporting pressure in response to rotation of the rotary member.
Furthermore, the rotary member positioned in the upper portion of the motor comprises a part of the thrust bearing. Therefore, posture-control during rotation is facilitated compared with the situation in which rotation is supported by a shaft descending from the rotary memberxe2x80x94for example, such as wherein a thrust plate is utilized. At the same time, susceptibility to margin of error in the elements comprising the thrust bearing, as well as in the precision and strength of the shaft and the rotary member connections, is slight, which facilitates assembly and enables improved productivity of the motors. Further, within the tolerance ranges of the superficial precision of the rotary member bottom face, and of the sleeve upper end face that compose the thrust bearing, the micro-gap between the thrust bearing can be set smaller (narrower). This boosts bearing rigidity of the thrust bearing, and improves the thrust load-bearing pressure.
Employing the foregoing storage disk drive motor, moreover, enables a storage disk drive device of the present invention to be slimmed, readily manufactured and assembled, lowered cost, and low power-consuming.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description in conjunction with the accompanying drawings.